Take-Over Performance and Safety Analysis Under Different Scenarios and Secondary Tasks in Conditionally Automated Driving

In conditionally automated driving, the driver is required to take-over control of a vehicle if a take-over request is issued due to possible system limitations. This study investigates the effect of roadway environments and secondary tasks on take-over performance and safety. The experiment was conducted in a real vehicle-based driving simulator. Participants experienced three different traffic scenarios, including a non-critical scenario and two critical scenarios. Manual driving, a 1-back cognitive secondary task and a letter game task were each tested in each scenario. Results indicate that different driving scenarios and secondary tasks impact take-over characteristics; in particular, they have a strong effect on take-over time and driver workload, which impacts take-over safety. Specifically, the steering reaction was generally slower than the braking reaction, indicating that lateral operation requires more cognitive and decision-making time. In extreme cases, braking operation alone was insufficient to ensure safety, and steering operation was required. When obstacles were difficult to detect, or when the driver was engaged in a visual secondary task, the steering reaction time increased significantly. This study provides data for take-over safety evaluations and best practices of conditionally automated driving.